Transmission type liquid crystal display having an organic interlayer elements film between pixel electrodes and switching

ABSTRACT

The transmission type liquid crystal display device of this invention includes: gate lines; source lines; and switching elements each arranged near a crossing of each gate line and each source line, a gate electrode of each switching element being connected to the gate line, a source electrode of the switching element being connected to the source line, and a drain electrode of the switching element being connected to a pixel electrode for applying a voltage to a liquid crystal layer, wherein an interlayer insulating film formed of an organic film with high transparency is provided above the switching element, the gate line, and the source line, and wherein the pixel electrode formed of a transparent conductive film is provided on the interlayer insulating film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a transmission type liquidcrystal display device which includes switching elements such as thinfilm transistors (hereinafter, referred to as “TFTs”) as addressingelements and is used for displays of computers, TV sets, and the like,and a method for fabricating such a transmission type liquid crystaldisplay device.

[0003] 2. Description of the Related Art

[0004]FIG. 16 is a circuit diagram of a conventional transmission typeliquid crystal display device provided with an active matrix substrate.

[0005] Referring to FIG. 16, the active matrix substrate includes aplurality of pixel electrodes 1 arranged in a matrix and TFTs 2 used asswitching elements connected to the respective pixel electrodes 1. Gateelectrodes of the TFTs 2 are connected to gate lines 3 for supplying ascanning (gate) signal, so that the gate signal can be input into thegate electrodes to control the driving of the TFTs 2. Source electrodesof the TFTs 2 are connected to source lines 4 for supplying an image(data) signal, so that the data signal can be input into thecorresponding pixel electrodes 1 via the TFTs when the TFTs are beingdriven. The gate lines 3 and the source lines 4 run adjacent to thepixel electrodes 1 and are arranged in a matrix to cross each other.Drain electrodes of the TFTs 2 are connected to the respective pixelelectrodes 1 and storage capacitors 5. Counter electrodes of the storagecapacitors 5 are connected to common lines 6. The storage capacitor 5 isused for holding a voltage applied to a liquid crystal layer. Thestorage capacitor is provided in parallel to a liquid crystal capacitorwhich includes the liquid crystal layer sandwiched between a pixelelectrode provided on an active matrix substrate and a counter electrodeprovided on a counter substrate.

[0006]FIG. 17 is a sectional view of a one-TFT portion of the activematrix substrate of the conventional liquid crystal display device.

[0007] Referring to FIG. 17, a gate electrode 12 connected to the gateline 3 shown in FIG. 16 is formed on a transparent insulating substrate11. A gate insulating film 13 is formed covering the gate electrode 12.A semiconductor layer 14 is formed on the gate insulating film 13 so asto overlap the gate electrode 12 via the gate insulating film 13, and achannel protection layer 15 is formed on the center of the semiconductorlayer 14. n⁺-Si layers as a source electrode 16 a and a drain electrode16 b are formed covering the end portions of the channel protectionlayer 15 and portions of the semiconductor layer 14, so that they areseparated from each other at the top of the channel protection layer 15.A metal layer 17 a which is to be the source line 4 shown in FIG. 16 isformed to overlap the source electrode 16 a as one of the n⁺-Si layers.A metal layer 17 b is formed to overlap the drain electrode 16 b as theother n⁺-Si layer so as to connect the drain electrode 16 b and thepixel electrode 1. An interlayer insulating film 18 is formed coveringthe TFT 2, the gate line 3, and the source line 4.

[0008] A transparent conductive film is formed on the interlayerinsulating film 18 to constitute the pixel electrode 1. The transparentconductive film is connected to the metal layer 17 b which is in contactwith the drain electrode 16 b of the TFT 2 via a contact hole 19 formedthrough the interlayer insulating film 18.

[0009] Thus, since the interlayer insulating film 18 is formed betweenthe pixel electrode 1 and the underlying layers including the gate andsource lines 3 and 4, it is possible to overlap the pixel electrode 1with the lines 3 and 4. Such a structure is disclosed in JapaneseLaid-Open Patent Publication No. 58-172685, for example. With thisstructure, the aperture ratio improves and, since the electric fieldgenerated by the lines 3 and 4 is shielded, the occurrence ofdisclination can be minimized.

[0010] Conventionally, the interlayer insulating film 18 is formed bydepositing an inorganic material such as silicon nitride (SiN) to athickness of about 500 nm by chemical vapor deposition (CVD).

[0011] The above conventional liquid crystal display device hasdisadvantages as follows.

[0012] When a transparent insulating film made of SiN_(x), SiO₂,TaO_(x), and the like is formed on the interlayer insulating film 18 byCVD or sputtering, the surface of the film directly reflects the surfaceprofile of the underlying film, i.e., the interlayer insulating film 18.Therefore, when the pixel electrode 1 is formed on the transparentinsulating film, steps will be formed on the pixel electrode 1 if theunderlying film has steps, causing disturbance in the orientation ofliquid crystal molecules. Alternatively, the interlayer insulating film18 may be formed by applying an organic material such as polyimide toobtain a flat pixel portion. In such a case, however, in order to formthe contact holes for electrically connecting the pixel electrodes andthe drain electrodes, a series of steps including photo-patterning usinga photoresist as a mask, etching for forming the contact holes, andremoval of the photoresist are required. A photosensitive polyimide filmmay be used to shorten the etching and removal steps. In this case,however, the resultant interlayer insulating film 18 appears colored.This is not suitable for a liquid crystal display device requiring highlight transmission and transparency.

[0013] The other disadvantage is as follows. When the pixel electrode 1overlaps the gate line 3 and the source line 4 via the interlayerinsulating film 18, the capacitances between the pixel electrode 1 andthe gate line 3 and between the pixel electrode 1 and the source line 4increase. In particular, when an inorganic film made of silicon nitrideand the like is used as the interlayer insulating film 18, thedielectric constant of such a material is as high as 8 and, since thefilm is formed by CVD, the thickness of the resultant film is as smallas about 500 nm. With such a thin interlayer insulating film, thecapacitances between the pixel electrode 1 and the lines 3 and 4 arelarge. This causes the following problems (1) and (2). Incidentally, inorder to obtain a thicker inorganic film made of silicon nitride and thelike, an undesirably long time is required in the aspect of thefabrication process.

[0014] (1) When the pixel electrode 1 overlaps the source line 4, thecapacitance between the pixel electrode 1 and the source line 4 becomeslarge. This increases the signal transmittance, and thus a data signalheld in the pixel electrode 1 during a holding period fluctuatesdepending on the potential thereof. As a result, the effective voltageapplied to the liquid crystal in the pixel varies, causing, inparticular, vertical crosstalk toward a pixel adjacent in the verticaldirection in the actual display.

[0015] In order to reduce the influence of the capacitance between thepixel electrode 1 and the source line 4 appearing on the display,Japanese Laid-Open Patent Publication No. 6-230422 proposes a drivingmethod where the polarity of a data signal to be supplied to the pixelsis inverted every source line. This driving method is effective for ablack-and-white display panel where the displays (i.e., data signals) ofadjacent pixels are highly correlated with each other. However, it isnot effective for a color display panel for normal notebook typepersonal computers and the like where pixel electrodes are arranged in avertical stripe shape (in color display, a square pixel is divided intothree vertically long rectangular picture elements representing R, G,and B, forming a vertical stripe shape). The display color of pixelsconnected to one source line is different from that of pixels connectedto an adjacent source line. Accordingly, the proposed driving method ofinverting the polarity of the data signal every source line is noteffective in reducing crosstalk for the general color display, though itis effective for the black-and-white display.

[0016] (2) When the pixel electrode 1 overlaps the gate line 3 fordriving the pixel, the capacitance between the pixel electrode 1 and thegate line 3 becomes large, increasing the feedthrough of the writevoltage to the pixel due to a switching signal for controlling the TFT2.

SUMMARY OF THE INVENTION

[0017] The transmission type liquid crystal display device of thisinvention includes: gate lines; source lines; and switching elementseach arranged near a crossing of each gate line and each source line. Agate electrode of each switching element is connected to the gate line,a source electrode of the switching element is connected to the sourceline, and a drain electrode of the switching element is connected to apixel electrode for applying a voltage to a liquid crystal layer,wherein an interlayer insulating film formed of an organic film withhigh transparency is provided above the switching element, the gateline, and the source line. The pixel electrode, formed of a transparentconductive film, is provided on the interlayer insulating film.

[0018] In one embodiment of the invention, the device further includes aconnecting electrode for connecting the pixel electrode and the drainelectrode, wherein the interlayer insulating film is provided above theswitching element, the gate line, the source line, and the connectingelectrode. The pixel electrode is formed on the interlayer insulatingfilm so as to overlap at least the gate line or the source line at leastpartially, and the connecting electrode and the pixel electrode areconnected with each other via a contact hole formed through theinterlayer insulating film.

[0019] In one embodiment of the invention, the interlayer insulatingfilm is made of a photosensitive acrylic resin.

[0020] In one embodiment of the invention, the interlayer insulatingfilm is made of a resin which is made transparent by optical or chemicaldecoloring treatment.

[0021] In one embodiment of the invention, the pixel electrode and atleast one of the source line and the gate line overlap each other by 1μm or more in a line width direction.

[0022] In one embodiment of the invention, the thickness of theinterlayer insulating film is 1.5 μm or more.

[0023] In one embodiment of the invention, the connecting electrode isformed of a transparent conductive film.

[0024] In one embodiment of the invention, the device further includes astorage capacitor for holding a voltage applied to the liquid crystallayer, wherein the contact hole is formed above either an electrode ofthe storage capacitor or the gate line.

[0025] In one embodiment of the invention, a metal nitride layer isformed below the contact hole to connect the connecting electrode andthe pixel electrode.

[0026] In one embodiment of the invention, the device further includes astorage capacitor for holding a voltage applied to the liquid crystallayer, wherein a capacitance ratio represented by expression (1):

[0027]Capacitance ratio=C _(sd)/(C _(sd) +C _(ls) +C _(s))   (1)

[0028] is 10% or less, wherein C_(sd) denotes a capacitance valuebetween the pixel electrode and the source line, C_(ls) denotes acapacitance value of a liquid crystal portion corresponding to eachpixel in an intermediate display state, and C_(s) denotes a capacitancevalue of the storage capacitor of each pixel.

[0029] In one embodiment of the invention, the shape of the pixelelectrode is rectangular with a side parallel to the gate line beinglonger than a side parallel to the source line.

[0030] In one embodiment of the invention, the device further includes adriving circuit for supplying to the source line a data signal of whichpolarity is inverted for every horizontal scanning period, and the datasignal is supplied to the pixel electrode via the switching element.

[0031] In one embodiment of the invention, the device further includes astorage capacitor for maintaining a voltage applied to the liquidcrystal layer, the storage capacitor including: a storage capacitorelectrode; a storage capacitor counter electrode; and an insulating filmtherebetween; wherein the storage capacitor electrode is formed in thesame layer as either the source line or the connecting electrode.

[0032] In one embodiment of the invention, the storage capacitor counterelectrode is formed of a part of the gate line.

[0033] In one embodiment of the invention, the pixel electrode and thestorage capacitor electrode are connected via the contact hole formedabove the storage capacitor electrode.

[0034] In one embodiment of the invention, the contact hole is formedabove either the storage capacitor counter electrode or the gate line.

[0035] In one embodiment of the invention, the interlayer insulatingfilm is formed of a photosensitive resin containing a photosensitiveagent which has a reactive peak at the i line (365 nm).

[0036] According to another aspect of the invention, a method forfabricating a transmission type liquid crystal display device isprovided. The method includes the steps of: forming a plurality ofswitching elements in a matrix on a substrate; forming a gate lineconnected to a gate electrode of each switching element and a sourceline connected to a source electrode of the switching element, the gateline and the source line crossing each other; and forming a connectingelectrode formed of a transparent conductive film connected to a sourceelectrode of the switching element. The method further includes formingan organic film with high transparency above the switching elements, thegate lines, the source lines, and the connecting lines by a coatingmethod and patterning the organic film to form an interlayer insulatingfilm and contact holes through the interlayer insulating film to reachthe connecting electrodes. The method also includes the step of formingpixel electrodes formed of transparent conductive films on theinterlayer insulating film and inside the contact holes so that eachpixel electrode overlaps at least either the gate line or the sourceline at least partially.

[0037] In one embodiment of the invention, the patterning of the organicfilm is conducted by either one of the following steps: exposing theorganic film to light and developing the exposed organic film, oretching the organic film by using a photoresist on the organic film asan etching mask.

[0038] In one embodiment of the invention, the patterning of the organicfilm includes the steps of: forming a photoresist layer containingsilicon on the organic film; patterning the photoresist layer; andetching the organic film by using the patterned photoresist layer as anetching mask.

[0039] In one embodiment of the invention, the patterning of the organicfilm includes the steps of: forming a photoresist layer on the organicfilm; coating a silane coupling agent on the photoresist layer andoxidizing the coupling agent; patterning the photoresist layer; andetching the organic film by using the patterned photoresist layercovered with the oxidized coupling agent as an etching mask.

[0040] In one embodiment of the invention, the etching step is a step ofdry etching using an etching gas containing at least one of CF₄, CF₃Hand SF₆.

[0041] In one embodiment of the invention, the organic film is formed byusing a photosensitive transparent acrylic resin which dissolves in adeveloping solution when exposed to light, and the interlayer insulatingfilm and the contact holes are formed by exposing the photosensitivetransparent acrylic resin to light and developing the photosensitivetransparent acrylic resin.

[0042] In one embodiment of the invention, the method further includesthe step of, after the light exposure and development of the organicfilm, exposing the entire substrate to light for reacting aphotosensitive agent contained in the photosensitive transparent acrylicresin, thereby decoloring the photosensitive transparent acrylic resin.

[0043] In one embodiment of the invention, a base polymer of thephotosensitive transparent acrylic resin includes a copolymer havingmethacrylic acid and glycidyl methacrylate and the photosensitivetransparent acrylic resin contains a quinonediazide positive-typephotosensitive agent.

[0044] In one embodiment of the invention, the photosensitivetransparent acrylic resin for forming the interlayer insulating film hasa light transmittance of 90% or more for light with a wavelength in therange of about 400 nm to about 800 nm.

[0045] In one embodiment of the invention, the organic film has athickness of about 1.5 μm or more.

[0046] In one embodiment of the invention, the method further includesthe step of, before the formation of the organic film, irradiating withultraviolet light a surface of the substrate where the organic film isto be formed.

[0047] In one embodiment of the invention, the method further includesthe step of, before the formation of the organic film, applying a silanecoupling agent on a surface of the substrate where the organic film isto be formed.

[0048] In one embodiment of the invention, the material for forming theorganic film contains a silane coupling agent.

[0049] In one embodiment of the invention, the silane coupling agentincludes at least one of hexamethyl disilazane, dimethyl diethoxysilane, and n-buthyl trimethoxy.

[0050] In one embodiment of the invention, the method further includesthe step of, before the formation of the pixel electrode, ashing thesurface of the interlayer insulating film by an oxygen plasma.

[0051] In one embodiment of the invention, the ashing step is conductedafter the formation of the contact holes.

[0052] In one embodiment of the invention, the interlayer insulatingfilm includes a thermally curable material and the interlayer insulatingfilm is cured before the ashing step.

[0053] In one embodiment of the invention, the thickness of the ashedportion of the interlayer insulating film is in the range of about 100to 500 nm.

[0054] In one embodiment of the invention, the thickness of the pixelelectrode is about 50 nm or more.

[0055] In one embodiment of the invention, the interlayer insulatingfilm is formed by developing the photosensitive transparent acrylicresin with tetramethyl ammonium hydroxyoxide developing solution with aconcentration of about 0.1 mol % to about 1.0 mol %.

[0056] In one embodiment of the invention, the method further includesthe step of, after the formation of the contact holes through theinterlayer insulating film, decoloring the interlayer insulating film byirradiating the interlayer insulating film with ultra-violet light.

[0057] In one embodiment of the invention, the method further includesthe step of, before the formation of the organic film, forming a siliconnitride film on a surface of the substrate where the organic film is tobe formed.

[0058] Thus, the invention described herein makes possible the advantageof (1) providing a transmission type liquid crystal display device whereflat pixel electrodes overlap respective lines to improve the apertureratio of the liquid crystal display, minimize disturbance in theorientation of liquid crystal molecules, and simplify the fabricationprocess. Furthermore, and the influence of the capacitance between thepixel electrodes and the lines appearing on the display, such ascrosstalk, can be reduced to achieve a good display. The inventiondescribed herein also makes possible the advantage of (2) providing amethod for fabricating such a transmission type liquid crystal displaydevice.

[0059] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 is a plan view of a one-pixel portion of an active matrixsubstrate of a transmission type liquid crystal display device ofExample 1 according to the present invention.

[0061]FIG. 2 is a sectional view taken along line A-A′ of FIG. 1.

[0062]FIG. 3 is a plan view of a one-pixel portion of an active matrixsubstrate of a transmission type liquid crystal display device ofExample 3 according to the present invention.

[0063]FIG. 4 is a sectional view taken along line B-B′ of FIG. 3.

[0064]FIG. 5 is a partial sectional view of an active matrix substrateof a transmission type liquid crystal display device of Example 4according to the present invention.

[0065]FIG. 6 is a graph illustrating the relationship between the liquidcrystal charging rate difference and the capacitance ratio fortransmission type liquid crystal display devices of Examples 5 and 6 anda conventional liquid crystal display device.

[0066]FIGS. 7A and 7B are waveforms of data signals in the cases of 1Hinversion driving in Examples 5 and 6 and conventional field inversiondriving, respectively.

[0067]FIG. 8 is a graph illustrating the relationship between the liquidcrystal capacitance ratio and the overlap width for the transmissiontype liquid crystal display device of Example 5.

[0068]FIG. 9 is a plan view of a one-pixel portion of an active matrixsubstrate of a transmission type liquid crystal display device ofExample 7 according to the present invention.

[0069]FIG. 10 is a sectional view taken along line C-C′ of FIG. 9.

[0070]FIG. 11 is a graph illustrating the variation in the transmittancebefore and after light exposure of an acrylic resin, depending on thewavelength (nm) of transmitted light for the transmission type liquidcrystal display device of Example 7.

[0071]FIG. 12 is a circuit diagram of a C_(s)-on-gate type liquidcrystal display device.

[0072]FIG. 13 is a plan view of a one-pixel portion of an active matrixsubstrate obtained by applying the structure of Example 3 to the liquidcrystal display device shown in FIG. 12.

[0073]FIG. 14 is a plan view of a one-pixel portion of an active matrixsubstrate of a transmission type liquid crystal display device ofExample 10 according to the present invention.

[0074]FIG. 15 is a sectional view taken along line D-D′ of FIG. 14.

[0075]FIG. 16 is a circuit diagram of a conventional liquid crystaldisplay device provided with an active matrix substrate.

[0076]FIG. 17 is a sectional view of a one-pixel portion of the activematrix substrate of the conventional liquid crystal display device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077] The present invention will be described by way of examples withreference to the accompanying drawings.

[0078] (Example 1)

[0079]FIG. 1 is a plan view of a one-pixel portion of an active matrixsubstrate of the transmission type liquid crystal display device ofExample 1 according to the present invention.

[0080] Referring to FIG. 1, the active matrix substrate includes aplurality of pixel electrodes 21 (within a bold line) arranged in amatrix. Gate lines 22 for supplying a scanning (gate) signal and sourcelines 23 for supplying an image (data) signal run surround theperipheries of the pixel electrodes 21 and cross each other. Theperipheries of each pixel electrode 21 overlap the gate lines 22 and thesource lines 23. A TFT 24 acting as a switching element connected to thecorresponding pixel electrode 21 is formed at a crossing of the gateline 22 and the source line 23. A gate electrode of the TFT 24 isconnected to the gate line 22 so that a gate signal can be input intothe gate electrode to control the driving of the TFT 24. A sourceelectrode of the TFT 24 is connected to the source line 23 so that adata signal can be input into the source electrode. A drain electrode ofthe TFT 24 is connected to the pixel electrode 21 via a connectingelectrode 25 and a contact hole 26. The drain electrode is alsoconnected to an electrode of a storage capacitor (a storage capacitorelectrode 25 a) via the connecting electrode 25. The other electrode ofthe storage capacitor, a storage capacitor counter electrode 27, isconnected to a common line (element 6 in FIG. 16).

[0081]FIG. 2 is a sectional view of the active matrix substrate takenalong line A-A′ of FIG. 1.

[0082] Referring to FIG. 2, a gate electrode 32 connected to the gateline 22 shown in FIG. 1 is formed on a transparent insulating substrate31. A gate insulating film 33 is formed covering the gate electrode 32.A semiconductor layer 34 is formed on the gate insulating film 33 so asto overlap the gate electrode 32 via the gate insulating film 33, and achannel protection layer 35 is formed on the center of the semiconductorlayer 34. n⁺-Si layers as a source electrode 36 a and a drain electrode36 b are formed covering the end portions of the channel protectionlayer 35 and portions of the semiconductor layer 34, so that they areseparated from each other by a portion of the channel protection layer35. A transparent conductive film 37 a and a metal layer 37 b which areto be the double-layer source line 23 shown in FIG. 1 are formed tooverlap the source electrode 36 a as one of the n⁺-Si layers. Atransparent conductive film 37 a′ and a metal layer 37 b′ are formed tooverlap the drain electrode 36 b as the other n⁺-Si layer. Thetransparent conductive film 37 a′ extends to connect the drain electrode36 b and the pixel electrode 21 and also serves as the connectingelectrode 25 which is connected to the storage capacitor electrode 25 aof the storage capacitor. An interlayer insulating film 38 is formedcovering the TFT 24, the gate line 22, the source line 23, and theconnecting electrode 25.

[0083] A transparent conductive film is formed on the interlayerinsulating film 38 to constitute the pixel electrode 21. The pixelelectrode 21 is connected to the drain electrode 36 b of the TFT 24 viathe contact hole 26 formed through the interlayer insulating film 38 andthe transparent conductive film 37 a′ which is the connecting electrode25.

[0084] The active matrix substrate with the above structure isfabricated as follows.

[0085] First, the gate electrode 32, the gate insulating film 33, thesemiconductor layer 34, the channel protection layer 35, and the n⁺-Silayers as the source electrode 36 a and the drain electrode 36 b aresequentially formed in this order on the transparent insulatingsubstrate 31 such as a glass substrate. This film formation step can beconducted following a conventional method for fabricating an activematrix substrate.

[0086] Thereafter, the transparent conductive films 37 a and 37 a′ andthe metal layers 37 b and 37 b′ constituting the source line 23 and theconnecting electrode 25 are sequentially formed by sputtering and arepatterned into a predetermined shape.

[0087] A photosensitive acrylic resin is applied to the resultantsubstrate to a thickness of 3 μm, for example, by spin coating to formthe interlayer insulating film 38. The resultant resin layer is exposedto light according to a predetermined pattern and developed with analkaline solution. Only portions of the resin layer exposed to light areetched with the alkaline solution, forming the contact holes 26 throughthe interlayer insulating film 38.

[0088] Subsequently, a transparent conductive film is formed on theresultant substrate by sputtering and is patterned to form the pixelelectrodes 21. Each pixel electrode 21 is thus connected to thecorresponding transparent conductive film 37 a′ which is in contact withthe drain electrode 36 b of the TFT 24 via the contact hole 26 formedthrough the interlayer insulating film 38. In this way, the activematrix substrate of this example is fabricated.

[0089] The thus-fabricated active matrix substrate includes the thickinterlayer insulating film 38 between the pixel electrode 21 and theunderlying layers including the gate line 22, the source line 23, andthe TFT 24. With this thick interlayer insulating film, it is possibleto overlap the pixel electrode 21 with the gate and source lines 22 and23 and the TFT 24. Also, the surface of the pixel electrode 21 can bemade flat. As a result, when the transmission type liquid crystaldisplay device including the thus-fabricated active matrix substrate anda counter substrate with a liquid crystal layer therebetween iscompleted, the aperture ratio of this device can be improved. Also,since the electric field generated at the lines 22 and 23 can beshielded, the occurrence of disclination can be minimized.

[0090] The acrylic resin constituting the interlayer insulating film 38has a dielectric constant of 3.4 to 3.8 which is lower than that of aninorganic film (e.g., the dielectric constant of silicon nitride is 8)and a high transparency. Also, since the spin coating is employed, athickness as large as 3 μm can be easily obtained. This reduces thecapacitances between the gate line 22 and the pixel electrode 21 andbetween the source lines 23 and the pixel electrodes 21, lowering thetime constant. As a result, the influence of the capacitances betweenthe lines 22 and 23 and the pixel electrode 21 appearing on the display,such as crosstalk, can be reduced, and thus a good and bright displaycan be obtained.

[0091] The contact hole 26 can be formed into a sharp tapered shape bythe patterning including the exposure to light and the alkalinedevelopment. This facilitates a better connection between the pixelelectrode 21 and the transparent conductive film 37 a′.

[0092] Further, since the photosensitive acrylic resin is used, thethick film having a thickness of several micrometers can be easilyformed by spin coating. No photoresist process is required at thepatterning step. This is advantageous in production. Though the acrylicresin used as the interlayer insulating film 38 is colored before thecoating, it can be made transparent optically by exposing the entiresurface to light after the patterning step. The resin can also be madetransparent chemically.

[0093] In this example, the photosensitive resin used as the interlayerinsulating film 38 is, in general, exposed to light from a mercury lampincluding the emission spectrum of the i line (wavelength: 365 nm), an hline (wavelength: 405 nm), and a g line (wavelength: 436 nm). The i linehas the highest energy (i.e., the shortest wavelength) among theseemission lines, and therefore it is desirable to use a photosensitiveresin having a reactive peak (i.e., absorption peak) at the i line. Thismakes it possible to form the contact holes with high precision, andmoreover, since the peak is farthest from the visible light, coloringcaused by the photosensitive agent can be minimized. A photosensitiveresin reactive to ultraviolet light having short wavelength emitted froman excimer laser can also be used. By using such an interlayerinsulating film substantially free from coloring, the transmittance ofthe resultant transmission type liquid crystal display device can beincreased. Accordingly, the brightness of the liquid crystal display canbe increased or the power consumption of the liquid crystal display canbe reduced by saving the amount of light needed from a backlight.

[0094] Since the thickness of the interlayer insulating film 38 is aslarge as several micrometers, thicker than that in conventional liquidcrystal display, a resin with a transmittance as high as possible ispreferably used. The visual sensitivity of a human eye for blue is alittle lower than those for green and red. Accordingly, even if thespectral transmittance of the film has slightly lower transmittance forblue light than that for green and red light, the display quality willbe not substantially deteriorated. Though the thickness of theinterlayer insulating film 38 was made 3 μm in this example, it is notlimited to 3 μm. The thickness of the interlayer insulating film may beset depending on the transmittance and the dielectric constant of thefilm. In order to reduce the capacitance, the thickness is preferablyequal to or grater than about 1.5 μm, more preferably equal to or graterthan about 2.0 μm.

[0095] In this example, the transparent conductive film 37 a′ is formedas the connecting electrode 25 connecting the drain electrode 36 b ofeach TFT 24 and the corresponding pixel electrode 21. This isadvantageous in the following points. In the conventional active matrixsubstrate, the connecting electrode is composed of a metal layer. Whensuch a metal connecting electrode is formed in the aperture portion, theaperture ratio is lowered. In order to overcome this problem, theconnecting electrode is conventionally formed above the TFT or the drainelectrode of the TFT. The contact hole is formed above the connectingelectrode through the interlayer insulating film to connect the drainelectrode of the TFT and the pixel electrode. With this conventionalstructure, however, when the TFT is made smaller to improve the apertureratio, for example, it is not possible to accommodate the entire contacthole above the smaller TFT. As a result, the aperture ratio is notimproved. When the thickness of the interlayer insulating film is madeas large as several micrometers, the contact hole should be tapered inorder to connect the pixel electrode and the underlying connectingelectrode, and a large-size connecting electrode is required in the TFTregion. For example, when the diameter of the contact hole is 5 μm, thesize of the connecting electrode should be about 14 μm in considerationof the tapered contact hole and the alignment allowance. In theconventional active matrix substrate, if a TFT with a size smaller thanthis value is realized, the oversized connecting electrode causes a newproblem of lowering the aperture ratio. In contrast, in the activematrix substrate of this example, since the connecting electrode 25 iscomposed of the transparent conductive film 37 a′, no trouble oflowering the aperture ratio arises. Further, in this example, theconnecting electrode 25 extends to connect the drain electrode 36 b ofthe TFT and the storage capacitor electrode 25 a of the storagecapacitor formed by the transparent conductive film 37 a′. Since theextension is also formed of the transparent conductive film 37 a′, itdoes not lower the aperture ratio, either.

[0096] In this example, the source line 23 is of a double-layerstructure composed of the transparent conductive layer 37 a and themetal layer 37 b. If part of the metal layer 37 b is defective, thesource line 23 can remain electrically conductive through thetransparent conductive film 37 a, so that the occurrence ofdisconnection of the source line 23 can be reduced.

[0097] (Example 2)

[0098] In Example 2, another method for forming the interlayerinsulating film 38 will be described.

[0099] The fabrication process until the transparent conductive films 37a and 37 a′ and the metal layers 37 b and 37 b′ are formed by sputteringand patterned is the same as that described in Example 1. Then, in thisexample, a non-photosensitive organic thin film, is formed on theresultant structure by spin coating. A photoresist is then formed on thethin film and patterned. Using the patterned photoresist, the organicthin film is etched to obtain the interlayer insulating film 38 and thecontact holes 26 formed through the interlayer insulating film 38.Alternatively, the non-photosensitive organic thin film may be formed bya CVD, instead of spin coating.

[0100] Examples of the non-photosensitive organic thin film include athermally curable acrylic resin. More specifically, JSS-924 (2-componentsystem acrylic resin) and JSS-925 (1-component system acrylic resin)manufactured by Japan Synthetic Rubber Co., Ltd. can be used. Theseresins generally have a heat resistance of 280° C. or more. Using anon-photosensitive resin for the interlayer insulating film allows forfreer resin design. For example, polyimide resin can be used. Examplesof transparent and colorless polyimide resin include polyimides obtainedby the combination of acid anhydrides such as2,2-bis(dicarboxyphenyl)hexafluoropropylene acid anhydride,oxydiphthalic acid anhydride, and biphenyl tetracaboxylic acidanhydride, with meta-substituted aromatic diamines having a sulfonegroup and/or an ether group or diamines having a hexafluoropropylenegroup. These polyimide resins are disclosed in Fujita, et al., NittoGiho, Vol. 29, No. 1, pp. 20-28 (1991), for example. Among the abovetransparent and colorless polyimide resins, a resin containing both acidanhydride and diamine each having a hexafluoropropylene group has a hightransparency. Fluoric resins other than the above fluoric polyimides canalso be used. Fluoric materials have not only excellent colorlesstransparency but also a low dielectric constant and high heatresistance.

[0101] A photoresist containing silicon is preferably used as thephotoresist for the patterning of the interlayer insulating film made ofa non-photosensitive organic material. In the above etching, dry etchingis normally conducted using a gas containing CF₄, CF₃H, SF₆ and thelike. In this case, however, since the photoresist and the interlayerinsulating film are both organic resins, it is difficult to increase theselection ratio between these resins. This is especially true in thecase where the thickness of the interlayer insulating film is as largeas 1.5 μm or more which is nearly the same as that of the photoresist,as in this example. It is preferable that the materials havesufficiently different etching rates (i.e., selectivity). When anacrylic resin is used as the interlayer insulating film in combinationwith a common photoresist material (e.g., OFPR-800 produced by TokyoOhka Kogyo Co., Ltd.) is used, for example, the selection ratio is about1.5. In contrast, in this example, by using the photoresist containingsilicon, a selectivity with respect to the photosensitive acrylic resinof about 2.0 or more can be obtained. Therefore, patterning with highprecision is attained.

[0102] Alternatively, at the formation of the interlayer insulating filmby the patterning using a photoresist which does not contain silicon, asilane coupling agent (e.g., hexamethyl disilazane) may be applied tothe photoresist and the silane coupling agent layer is treated withoxygen plasma to form a silicon oxide film. As a result, the etchingrate of the photoresist is reduced, since the silicon oxide film on thephotoresist serves as a protection film. This method can be used incombination with the silicon containing photoresist.

[0103] The increase in the selection ratio by the above mentioned methodutilizing a silicon element is especially effective in the dry etchingusing a gas containing CF₄, CF₃H or SF₆.

[0104] The active matrix substrate with the thus-formed interlayerinsulating film 38 can also provide a high aperture ratio, as in Example1.

[0105] The non-photosensitive organic thin film used as the interlayerinsulating film 38 in this example has a low dielectric constant and ahigh transparency. The thickness can be as large as 3 μm. With the lowdielectric constant and the long distance between electrodes of thecapacitance, the capacitances between the gate line 22 and the pixelelectrode 21 and between the source line 23 and the pixel electrode 21can be reduced.

[0106] (Example 3)

[0107]FIG. 3 is a plan view of a one-pixel portion of an active matrixsubstrate of the transmission type liquid crystal display device ofExample 3 according to the present invention. FIG. 4 is a sectional viewtaken along line B-B′ of FIG. 3. Components having like functions andeffects are denoted by the same reference numerals as those in FIGS. 1and 2, and the description thereof is omitted.

[0108] In the active matrix substrate of this example, each contact hole26 a is formed above the storage capacitor electrode 25 a and thestorage capacitor counter electrode 27 of the storage capacitor of eachpixel. As described in Example 1, the storage capacitor electrode 25 aconstitutes the end portion of the connecting electrode 25 which isconnected to the drain electrode 36 b of the TFT 24. The other electrodeof the storage capacitor, the storage capacitor counter electrode 27, isconnected to a counter electrode formed on a counter substrate via thestorage capacitor common line 6 shown in FIG. 16. In other words, thecontact holes 26 a are formed above the storage capacitor common line 6which is composed of a light-shading metal film.

[0109] The above structure of the active matrix substrate of thisexample has the following advantages.

[0110] Since the thickness of the interlayer insulating film 38 is aslarge as 3 μm, for example, which is well comparable with the thicknessof a liquid crystal cell of 4.5 μm, light leakage tends to occur aroundthe contact holes 26 a due to a disturbance in the orientation of theliquid crystal molecules. If the contact holes 26 a are formed in theaperture portions of the transmission type liquid crystal displaydevice, the contrast is lowered due to the light leakage. On the otherhand, the active matrix substrate of this example is free from thistrouble because each contact hole 26 a is formed above the storagecapacitor electrode 25 a and the storage capacitor counter electrode 27as an end portion of the storage capacitor common line 6 composed of alight-shading metal film. In other words, as long as the contact hole 26a is formed above the storage capacitor common line 6 composed of alight-shading metal film, not in the aperture portion, any light leakagewhich may occur around the contact hole 26 a due to a disturbance in theorientation of the liquid crystal molecules will not result in loweringof the contrast. This also applies to the case where the storagecapacitor is formed using a portion of the adjacent gate line 22 as oneof electrodes thereof. In this case, the contact hole 26 a is formedabove the light-shading gate line 22 and thus lowering of the contrastcan be prevented.

[0111] In the active matrix substrate of this example, the connectingelectrode 25 for connecting the drain electrode 36 b of the TFT 24 andthe contact hole 26 a is composed of the transparent conductive film 37a′. Accordingly, the aperture ratio does not become lower by forming thecontact hole 26 a above the storage capacitor.

[0112] Thus, in this example, since the storage capacitor counterelectrode 27 formed under the contact hole 26 a shades light, lightleakage which may occur due to a disturbance in the orientation of theliquid crystal molecules does not influence the display. The size of thecontact hole 26 a is not necessarily so precise, allowing the hole to belarger and smoother. As a result, the pixel electrode 21 formed on theinterlayer insulating film 38 is continuous, not being interrupted bythe contact hole 26 a. This improves the production yield.

[0113] (Example 4)

[0114]FIG. 5 is a partial sectional view of an active matrix substrateof the transmission type liquid crystal display device of Example 4according to the present invention. Components having like functions andeffects are denoted by the same reference numerals as those in FIGS. 1to 4, and the description thereof is omitted.

[0115] In the active matrix substrate of this example, each contact hole26 b is formed through the interlayer insulating film 38 above thestorage capacitor common line 6. A metal nitride layer 41 is formed onthe portion of the transparent conductive film 37 a′ under each contacthole 26 b.

[0116] The above structure of the active matrix substrate of thisexample is advantageous in the following point.

[0117] Some troubles arise in the adhesion between the resin used forthe interlayer insulating film 38 and ITO (indium tin oxide) used forthe transparent conductive film or metal such as Ta and Al. For example,in the cleaning process after the formation of the contact hole 26 b, acleaning solvent tends to permeate from the contact hole into theinterface between the resin and the underlying transparent conductivefilm, causing the resin film to peel from the transparent conductivefilm. In order to overcome this trouble, according to the active matrixsubstrate of this example, the metal nitride layer 41 made of TaN, AlN,and the like which have good adhesion with the resin is formed on thetransparent conductive film under the contact hole. Accordingly, thepeeling of the resin film and other troubles in the adhesion can beprevented.

[0118] Any material can be used for the metal nitride layer 41 as longas it has good adhesion with the resin constituting the interlayerinsulating film 38, ITO and the like constituting the transparentconductive film 37 a′, and metal such as Ta and Al. Such a materialshould also be electrically conductive to electrically connect thetransparent conductive film 37 a′ and the pixel electrode 21.

[0119] (Example 5)

[0120] In Example 5, a method for driving the transmission type liquidcrystal display device according to the present invention will bedescribed.

[0121] In the transmission type liquid crystal display device accordingto the present invention, each pixel electrode overlaps thecorresponding lines via the interlayer insulating film. If the pixelelectrode does not overlap the corresponding lines but gaps are formedtherebetween, regions where no electric field is applied are formed inthe liquid crystal layer. This trouble can be avoided by overlapping thepixel electrode with the lines. The electric field also is not appliedto the regions of the liquid crystal layer corresponding to theboundaries of the adjacent pixel electrodes. However, light leakagewhich may occur at these regions can be blocked by the existence oflines. This eliminates the necessity of forming a black mask on acounter substrate in consideration of an error at the lamination of theactive matrix substrate and the counter substrate. This improves theaperture ratio. Also, since the electric field generated at the linescan be shielded, disturbances in the orientation of the liquid crystalmolecules can be minimized.

[0122] The overlap width should be set in consideration of a variationin the actual fabrication process. For example, it is preferably about1.0 μm or more.

[0123] Crosstalk occurs due to the capacitance between the pixelelectrode and the source line when the pixel electrode overlaps thesource line as described above. This lowers the display quality of theresultant transmission type liquid crystal display device. Inparticular, in a liquid crystal panel used for a notebook type personalcomputer where pixels are arranged in a vertical stripe shape, thedisplay is greatly influenced by the capacitance between the pixelelectrode and the source line. This is considered to be due to thefollowing reasons: (1) The capacitance between the pixel electrode andthe source line is relatively large since, in the vertical stripearrangement, the shape of the pixel electrode is rectangular having theside along the source line as the major side; (2) Since the displaycolor is different between adjacent pixels, there is little correlationbetween signals transmitted on the adjacent source lines. Thus, theinfluence of the capacitance cannot be cancelled between the adjacentsource lines.

[0124] According to the transmission type liquid crystal display deviceof the present invention, the interlayer insulating film which iscomposed of an organic thin film has a small dielectric constant and canbe easily thicker. Therefore, the capacitances between the pixelelectrodes and the lines can be reduced, as described above. In additionto this feature, according to the method for driving the transmissiontype liquid crystal display device of this example, the influence of thecapacitance between the pixel electrode and the source line can bereduced to minimize vertical crosstalk which occurs in notebook typepersonal computers.

[0125] The method of this example includes driving the transmission typeliquid crystal display device by inverting the polarity of the datasignal for every horizontal scanning period (hereinafter, this method isreferred to as “1H inversion driving”).

[0126]FIG. 6 shows the influences of the capacitance between the pixelelectrode and the source line upon the charging rate of the pixel in thecases of the 1H inversion driving and a driving method where thepolarity of the data signal is inverted every field (hereinafter, thismethod is referred to as “field inversion driving”). FIGS. 7A and 7Bshow the waveforms obtained by the 1H inversion driving and the fieldinversion driving, respectively.

[0127] In FIG. 6, the Y axis represents the charging rate differencewhich indicates the ratio of the effective value of the voltage appliedto the liquid crystal layer in the gray scale display portion when thegray scale is uniformly displayed to that when a black window pattern isdisplayed in the gray scale display at a vertical occupation of 33%. TheX axis represents the capacitance ratio which is proportional to thevariation in the voltage of the pixel electrode caused by thecapacitance between the pixel electrode and the source line, which isrepresented by expression (1) below:

Capacitance ratio=C _(sd)/(C_(sd) +C _(ls) +C _(s))   (1)

[0128] wherein C_(sd) denotes the capacitance value between the pixelelectrode and the source line, C_(ls) denotes the capacitance value ofthe liquid crystal portion corresponding to each pixel at the gray scaledisplay, and C_(s) denotes the capacitance value of the storagecapacitor of each pixel. The gray scale display refers to the displayobtained when the transmittance is 50%.

[0129] As is observed from FIG. 6, in the 1H inversion driving of thisexample, the influence of the capacitance between the pixel electrodeand the source line upon the effective voltage actually applied to theliquid crystal layer can be reduced to one-fifth to one-tenth of thatobtained in the field inversion driving when the capacitance value isthe same. This is because, in the 1H inversion driving, the polarity ofthe data signal is inverted at intervals sufficiently shorter than theperiod of one field during one field. This results in cancelling theinfluences of the positive signal and the negative signal on the displaywith each other.

[0130] A display test was conducted using a VGA panel with a diagonal of26 cm. From this test, it was observed that crosstalk was eminent whenthe charging rate difference was 0.6% or more, degrading the displayquality. This is shown by the dotted curve in FIG. 6. From the curve inFIG. 6, it is found that the capacitance ratio should be 10% or less inorder to obtain the charging rate difference of 0.6% or less.

[0131]FIG. 8 shows the relationships between the overlap amount betweenthe pixel electrode and the source line and the capacitance between thepixel electrode and the source line when the thickness of the interlayerinsulating film is used as a parameter. The VGA panel with a diagonal of26 cm was also used in this test. In the test, the acrylicphotosensitive resin (dielectric constant: 3.4) used in Example 1 wasused as the interlayer insulating film. In consideration of theprocessing precision, the overlap width between the pixel electrode andthe source line should be at least 1 μm. From FIGS. 6 and 8, it is foundthat the thickness of the interlayer insulating film should be 2.0 μm ormore to satisfy the overlap width of 1 μm and the charging ratedifference of 0.6% or less.

[0132] Thus, according to the 1H inversion driving of this example, agood display free from vertical crosstalk can be obtained withoutinverting the polarity of the signal on the adjacent source lines(source line inversion driving) when the pixel electrode overlaps thesource line. This method is therefore applicable to notebook typepersonal computers.

[0133] It has also been found that a dot inversion driving has similareffects to those obtained by the 1H inversion driving. The dot inversiondriving is a driving method where signals of the opposite polarities areinput into pixel electrodes adjacent each other in the transversedirection and also the polarity is inverted every horizontal scanningperiod. A source line inversion driving is also effective when thecapacitance ratio is sufficiently low as in the above case. Further,even in the color display operation where adjacent signals are nothighly correlated with each other, colored crosstalk may be suppressed,since the capacitance between the pixel electrode and the source line issufficiently reduced according to the present invention.

[0134] (Example 6)

[0135] In Example 6, another method for driving the transmission typeliquid crystal display device according to the present invention will bedescribed. In this method, the polarity of the voltage applied to theliquid crystal layer is inverted for every horizontal scanning period,and simultaneously the signal applied to the counter electrode is drivenby alternate current in synchronization with the inversion of thepolarity of the source signal. This AC driving of the counter electrodecan minimize the amplitude of the source signal.

[0136]FIG. 6 described in Example 5 also shows the curve obtained whenthe counter electrode is AC driven with an amplitude of 5 V. From FIG.6, it is observed that, since the 1H inversion driving is employed, thecharging rate difference is sufficiently small compared with the case ofthe field inversion driving, though it is larger by about 10 percentthan that obtained in Example 5 due to the AC driving of the counterelectrode in this example. As a result, a good display without verticalcrosstalk can be realized in the driving method of this example, as inthe previous example.

[0137] (Example 7)

[0138]FIG. 9 is a plan view of a one-pixel portion of an active matrixsubstrate of the transmission type liquid crystal display device ofExample 7.

[0139] In the transmission type liquid crystal display device of thisexample, each flat pixel electrode overlaps corresponding lines toimprove the aperture ratio of the liquid crystal display, minimizedisturbances in the orientation of the liquid crystal molecules, andsimplify the fabrication process. Also, the influence of thecapacitances between the pixel electrode and the lines appearing on thedisplay, such as crosstalk, is minimized thereby achieving a gooddisplay. In this example, an interlayer insulating film with hightransparency can be obtained. After the light exposure and developmentof the interlayer insulating film, the entire substrate is exposed tolight to react the remaining unnecessary photosensitive agent containedin the photosensitive transparent acrylic resin.

[0140] Referring to FIG. 9, the active matrix substrate includes aplurality of pixel electrodes 51 arranged in a matrix. Gate lines 52 andsource lines 53 run along the peripheries of the pixel electrodes 51 tocross each other. The peripheries of each pixel electrode 51 overlap thegate lines 52 and the source lines 53. A TFT 54 as a switching elementconnected to the corresponding pixel electrode 51 is formed at acrossing of the gate line 52 and the source line 53. A gate electrode ofthe TFT 54 is connected to the gate line 52 so that a gate signal isinput into the gate electrode to control the driving of the TFT 54. Asource electrode of the TFT 54 is connected to the source line 53 sothat a data signal can be input into the source electrode. A drainelectrode of the TFT 54 is connected to the corresponding pixelelectrode 51 via a connecting electrode 55 and a contact hole 56. Thedrain electrode is also connected to an electrode of a storagecapacitor, a storage capacitor electrode 55 a, via the connectingelectrode 55. The other electrode of the storage capacitor, a storagecapacitor counter electrode 57, is connected to a common line.

[0141]FIG. 10 is a sectional view of the active matrix substrate takenalong line C-C′ of FIG. 9.

[0142] Referring to FIG. 10, a gate electrode 62 connected to the gateline 52 shown in FIG. 9 is formed on a transparent insulating substrate61. A gate insulating film 63 is formed covering the gate electrode 62.A semiconductor layer 64 is formed on the gate insulating film 63 so asto overlap the gate electrode 62 via the gate insulating film 63, and achannel protection layer 65 is formed on the center of the semiconductorlayer 64. n⁺-Si layers as a source electrode 66 a and a drain electrode66 b are formed covering the end portions of the channel protectionlayer 65 and portions of the semiconductor layer 64, so that they areseparated from each other at the top of the channel protection layer 65.A transparent conductive film 67 a and a metal layer 67 b which are tobe the double-layer source line 53 shown in FIG. 9 are formed to overlapthe source electrode 66 a as one of the n⁺-Si layers. A transparentconductive film 67 a′ and a metal layer 67 b′ are formed to overlap thedrain electrode 66 b as the other n⁺-Si layer. The transparentconductive film 67 a′ extends to connect the drain electrode 66 b andthe pixel electrode 51 and also serves as the connecting electrode 55which is connected to the storage capacitor electrode 55 a. Aninterlayer insulating film 68 is formed covering the TFT 54, the gateline 52, the source line 53, and the connecting electrode 55. Theinterlayer insulating film 68 is made of a high-transparency acrylicresin (photosensitive transparent acrylic resin) which dissolves in adeveloping solution when exposed to light.

[0143] A transparent conductive film is formed on the interlayerinsulating film 68 to constitute the pixel electrode 51. The pixelelectrode 51 is connected to the drain electrode 66 b of the TFT 54 viathe contact hole 56 formed through the interlayer insulating film 68 andthe transparent conductive film 67 a′ which is the connecting electrode55.

[0144] The active matrix substrate with the above structure isfabricated as follows.

[0145] First, the gate electrode 62 made of Ta, Al, Mo, W, Cr, and thelike, the gate insulating film 63 made of SiN_(x), SiO₂, Ta₂O₅, and thelike, the semiconductor layer (intrinsic-Si) 64, the channel protectionlayer 65 made of SiN_(x), Ta₂O₅, and the like, the n⁺-Si layers as thesource electrode 66 a and the drain electrode 66 b are sequentiallyformed in this order on the transparent insulating substrate 61 such asa glass substrate.

[0146] Thereafter, the transparent conductive films 67 a and 67 a′ andthe metal layers 67 b and 67 b′ made of Ta, Al, MoW, Cr, and the likeconstituting the source line 53 and the connecting electrode 55 aresequentially formed by sputtering and are patterned into a predeterminedshape. In this example, as in the previous examples, the source line 53is of the double-layer structure composed of the transparent conductivefilm 67 a made of ITO and the metal film 67 b. With this structure, ifpart of the metal layer 67 b is defective, the source line 53 can remainelectrically conductive through the transparent conductive film 67 a, sothat the occurrences of disconnection of the source line 53 can bereduced.

[0147] A photosensitive acrylic resin is applied to the resultantstructure to a thickness of 2 μm, for example, by spin coating to formthe interlayer insulating film 68. The resultant resin layer is exposedto light according to a predetermined pattern and developed with analkaline solution. Only the portions exposed to light are etched withthe alkaline solution, which forms the contact holes 56 through theinterlayer insulating film 68.

[0148] Subsequently, a transparent conductive film is formed over theinterlayer insulating film 68 and the contact holes 56 by sputtering andis patterned to form the pixel electrodes 51. Thus, each pixel electrode51 is connected to the transparent conductive film 67 a′ which is incontact with the drain electrode 66 b of the TFT 54 via the contact hole56 formed through the interlayer insulating film 68. In this way, theactive matrix substrate of this example is fabricated.

[0149] The interlayer insulating film 68 of Example 7 is made of apositive-type photosensitive acrylic resin, which is a photosensitivetransparent acrylic resin with high transparency which dissolves in adeveloping solution after exposure to light.

[0150] The positive-type photosensitive acrylic resin is preferably amaterial composed of a copolymer of methacrylic acid and glycidylmethacrylate as a base polymer mixed with a naphthoquinone diazidepositive-type photosensitive agent, for example. Since this resincontains the glycidyl group, it can be crosslinked (cured) by heating.After curing, the resin has the properties of: a dielectric constant ofabout 3.4; and a transmittance of 90% or more for light with awavelength in the range of 400 to 800 nm. The resin can be decolored ina shorter time by being irradiated with iline (365 nm) ultravioletlight. Ultraviolet light other than the i line can be used forpatterning. Since the heat resistance of the photosensitive acrylicresin used in this example is generally 280° C., the degradation of theinterlayer insulating film can be suppressed by conducting the processsuch as the formation of the pixel electrodes after the formation of theinterlayer insulating film at a temperature in the range of about 250°C. to 280° C.

[0151] The formation of the interlayer insulating film 68 using theabove-described photosensitive acrylic resin with high transparency willbe described in detail.

[0152] First, a solution containing the photosensitive transparentacrylic material is applied to the substrate by spin coating, followedby a normal photo-patterning process including prebaking, patternexposure, alkaline development, and cleaning with pure water in thisorder.

[0153] Specifically, the interlayer insulating film 68 with a thicknessof 3 μm is formed by applying a solution containing the photosensitivetransparent acrylic resin to the resultant substrate by spin coating.More specifically, the acrylic resin with a viscosity of 29.0 cp isapplied at a spin rotation of 900 to 1100 rpm. This makes it possible toobtain flat pixel electrodes without steps unlike in the conventionalmethod, minimizing disturbances in the orientation of liquid crystalmolecules and improving the resultant display quality.

[0154] Subsequently, the resultant substrate is heated to about 100° C.to dry a solvent of the photosensitive transparent acrylic resin (e.g.,ethyl lactate, propylene glycol monomethyl ether acetate, etc.). Theresultant photosensitive acrylic resin is exposed to light according toa predetermined pattern and developed with an alkaline solution(tetramethyl ammonium hydroxyoxide, abbreviated to “TMAH”). The portionsof the substrate exposed to light are etched with the alkaline solution,forming the contact holes 56 through the interlayer insulating film 68.The concentration of the developing solution is preferably in the rangeof 0.1 to 1.0 mol % (in the case of TMAH). When the concentrationexceeds 1.0 mol %, the portions of the photosensitive transparentacrylic resin which are not exposed to light are also largely etched,making it difficult to control the thickness of the photosensitivetransparent acrylic resin. When the concentration of the developingsolution is as high as 2.4 mol %, altered substances from the acrylicresin are left in the etched portions as residues, causing contactfailure. When the concentration is less than 0.1 mol %, theconcentration largely varies as the developing solution is circulatedfor repeated use. This makes it difficult to control the concentration.Thereafter, the developing solution left on the substrate surface iswashed away with pure water.

[0155] As described above, the interlayer insulating film can be formedby spin coating. Accordingly, the thickness of the film which may beseveral micrometers can be made uniform easily by appropriatelyselecting the rotation of the spin coater and the viscosity of thephotosensitive transparent acrylic resin. The contact hole can be madeinto a smooth tapered shape by appropriately selecting the amount oflight exposure during the pattern exposure, the concentration of thedeveloping solution, and the developing time.

[0156] The resin may appear colored after the development depending onthe type and amount of the photosensitive agent (e.g., naphthoquinonediazide photosensitive agents and naphthoquinone diazide positive-typephotosensitive agents) contained in the photosensitive transparentacrylic resin. To avoid this problem, the entire substrate is exposed tolight to allow the remaining unnecessary colored photosensitive agentcontained in the resin to completely react, so as to eliminate lightabsorption in the visible region and thereby to make the acrylic resintransparent. Examples of the photosensitive agent include naphthoxydiazide positive-type photosensitive agents and naphthoquinone diazidephotosensitive agents.

[0157]FIG. 11 shows the variation in the light transmittance of thesurface of the acrylic resin with a thickness of 3 μm before and afterbeing exposed to light such as ultraviolet light, depending on thewavelength (nm) of the transmitted light. As is observed from FIG. 11,when the resin has not been exposed to light, the transmittance of theresin is 65% for transmitted light with a wavelength of 400 nm. Afterthe resin is exposed to light, the transmittance is improved to 90% ormore. In this case, the substrate was irradiated with light from thefront side thereof. This light exposure step can be shortened byirradiating the substrate with light from both the front side and theback side. This improves the throughput of the process.

[0158] Finally, the resultant substrate is heated to cure the resin bycrosslinking. More specifically, the substrate is placed on a hot plateor in a clean oven and heated to about 200° C. to cure the resin.

[0159] Thus, by using the photosensitive transparent resin, theinterlayer insulating film 68 and the contact holes 56 formed throughthe interlayer insulating film 68 for connecting the pixel electrodesand the drain electrodes of the switching elements can be formed only bythe photo-patterning without the conventional etching andresist-removing steps. This simplifies the fabrication process. Thethickness of the photosensitive transparent acrylic resin may be anydesired value in the range of 0.05 to 10 μm (3 μm in Example 7; notethat the light transmittance lowers and the coloring is more prominentas the thickness becomes larger) and can be made uniform byappropriately selecting the viscosity of the resin solution and therotation of the spin coater during spin coating.

[0160] Thereafter, ITO is deposited on the photosensitive transparentacrylic resin to a thickness of 50 to 150 nm by sputtering and ispatterned to form the pixel electrodes 51. The ITO film as each pixelelectrode 51 having a thickness of 50 nm or more effectively prevents anagent (e.g., dimethyl sulfoxide) used as a removing solution frompermeating from gaps of the surface of the ITO film into the resin andthe resin from expanding due to the permeation of the agent. The activematrix substrate of Example 7 is thus fabricated.

[0161] Thus, in this example, as in the previous examples, with theexistence of the interlayer insulating film 68, all the portions of thedisplay panel other than the source and gate line portions can be usedas pixel aperture portions. The resultant liquid crystal display deviceis bright with high transmittance and a large aperture ratio.

[0162] Moreover, with the existence of the interlayer insulating film68, the pixel electrodes can be made flat without being influenced bysteps formed by the underlying lines and switching elements. Thisprevents the occurrence of disconnection conventionally found at thesteps on the drain sides of the pixel electrodes, and thereby reducesthe number of defective pixels. Disturbances in the orientation ofliquid crystal molecules caused by the steps can also be prevented.Furthermore, since the source lines 53 and the pixel electrodes 51 areisolated from each other with the interlayer insulating film 68therebetween, the number of defective pixels conventionally caused bythe electrical leakage between the source lines 53 and the pixelelectrodes 51 can be reduced.

[0163] Further, in this example, the interlayer insulating film 68 canbe formed only by the resin formation step, instead of the filmformation step, the pattern formation step with a photoresist, theetching step, the resist removing step, and the cleaning stepconventionally required. This simplifies the fabrication process.

[0164] (Example 8)

[0165] In Example 8, the method for improving the adhesion between theinterlayer insulating film 68 and the underlying films described inExample 7 shown in FIGS. 9 and 10 will be described.

[0166] The adhesion of the photosensitive transparent acrylic resin asthe interlayer insulating film 68 with the underlying films may beinferior depending on the materials of the underlying films. In such acase, according to the method of this example, the surfaces of theunderlying films, i.e., the gate insulating film 63, the channelprotection film 65, the source electrode 66 a, the drain electrode 66 b,the transparent conductive films 67 a and 67 a′, and the metal films 67b and 67 b′ are exposed to ultraviolet light from an M-type mercury lamp(860 W) in an oxygen atmosphere before the application of thephotosensitive transparent acrylic resin, so as to roughen the surfaces.The interlayer insulating film 68 made of the photosensitive transparentacrylic resin is then formed on the roughened surfaces of the underlyingfilms. The subsequent steps are the same as those described in Example7. By this method, the adhesion between the photosensitive transparentacrylic resin and the surface-roughened underlying films improves. Thisovercomes the conventional problem of the film peeling at the interfacebetween the interlayer insulating film 68 made of the photosensitivetransparent acrylic resin and the underlying films. This conditionresults when an agent such as a mixture of hydrochloric acid and ironchloride for etching ITO, permeates into the interface.

[0167] Thus, by irradiating the substrate surface before the formationof the interlayer insulating film 68 with ultraviolet light, theadhesion between the interlayer insulating film 68 and the underlyingfilms improves. The resultant device can be stable despite furtherprocessing during the fabrication process.

[0168] An alternative method for improving the adhesion according to thepresent invention is to treat the surface to be coated with the resinwith a silane coupling agent before the coating with the resin. As thesilane coupling agent, hexamethyl disilazane, dimethyl diethoxy silane,n-buthyl trimethoxy silane, and the like are especially effective inimprovement of the adhesion. For example, in the case of adhesion withthe silicon nitride film, it has been found that the adhesion strengthof the treated surface improves by about 10% compared with that of thesurface not treated with the silane coupling agent. The problem that thepattern of the resin is damaged due to an internal stress generated bythe crosslinking of the resin, which sometimes occurs if the surface isnot so treated, is prevented by this treatment with the silane couplingagent.

[0169] The silane coupling agent may be blended in the resin before theapplication of the resin, instead of applying the agent to theunderlaying layer before the application of the resin. The same adhesioneffect can be obtained by this method. Specifically, when 1 wt % ofdimethyl diethoxy silane was added to the photosensitive acrylic resin,the adhesion strength of the resin with the silicon nitride film (i.e.,a under laying layer) improved by 70%.

[0170] (Example 9)

[0171] In Example 9, the method for improving the adhesion between theinterlayer insulating film 68 and the pixel electrode material formedthereon described in Example 7 and shown in FIGS. 9 and 10 will bedescribed.

[0172] After the formation of the interlayer insulating film 68 made ofthe photosensitive transparent acrylic resin in Example 7, the surfaceportion of the interlayer insulating film 68 with a thickness of 100 to500 nm is ashed in an oxygen plasma atmosphere using a dry etchingapparatus. More specifically, the surface of the acrylic resin is ashedin the oxygen plasma atmosphere using a parallel plane type plasmaetching apparatus under the conditions of a RF power of about 1.2 KW, apressure of about 800 m Torr, an oxygen flow rate of about 300 sccm, atemperature of 70° C., and a RF applying time of about 120 seconds. Bythis process, water and carbon dioxide are released from the surface ofthe acrylic resin by oxidation decomposition, and thus the surface isroughened.

[0173] Thereafter, ITO is deposited on the roughened photosensitivetransparent acrylic resin to a thickness of about 50 to about 150 nm bysputtering and patterned to form the pixel electrodes 51. The activematrix substrate is thus fabricated.

[0174] By this ashing, the adhesion between the pixel electrodes 51 andthe underlying roughened interlayer insulating film 68 made of thephotosensitive transparent acrylic resin greatly improves. Nodelamination at the interface thereof was caused by an application ofultrasound for cleaning the substrate. The above effect was not obtainedwhen the thickness of the ashed surface portion of the acrylic resin wasless than 100 nm. When it exceeds 500 nm, the decrease in the thicknessof the photosensitive transparent acrylic resin is so large that thevariation in the thickness of the resultant acrylic resin increases,causing display troubles. The improvement in the adhesion is obtained byusing any type of the dry etching apparatus including a barrel type anda RIE type.

[0175] Thus, by ashing the surface portion of the interlayer insulatingfilm 68 in the oxygen plasma atmosphere before the formation of thepixel electrodes, the adhesion between the interlayer insulating film 68and the pixel electrode material improves. The resultant device can bestable against further processing during the fabrication process. Inaddition, the ashing is also effective in removing residues from thecontact holes. This reduces the occurrence of disconnection in thecontact holes.

[0176] In this example, the ashing is conducted after the crosslinkingof the resin for the interlayer insulation film. This is advantageousfor conducting the ashing step in a more stable condition, since gas isgenerated in the crosslinking step.

[0177] (Example 10)

[0178]FIG. 14 is a plane view of an active matrix substrate of thetransmission type liquid crystal display device of Example 10 accordingto the present invention. FIG. 15 is a sectional view taken along lineD-D′ of FIG. 14. Components having like functions and effects aredenoted by the same reference numerals as those in FIGS. 1 and 2, andthe description thereof is omitted.

[0179] In the active matrix substrate of this example, the connectionsbetween each TFT 24 and the corresponding pixel electrode 21 and betweeneach storage capacitor electrode 25 a and the corresponding pixelelectrode 21 are effected via separate contact holes 26 a and 26 b,respectively. Also, in this example, each source line 23 is composed ofa single metal layer, though it may be of a multi-layer structure. Thestorage capacitor electrodes 25 a are formed of the same material asthat of the source lines 23 in the same step as in the previousexamples. The two contact holes 26 a and 26 b are formed above a metalelectrode 23 b connected to the drain electrode 36 b of the TFT andabove the storage capacitor electrode 25 a, respectively. That is, thesecontact holes 26 a and 26 b formed above the metal electrodes having alight-shading property.

[0180] The transmission type liquid crystal display device with theabove structure is advantageous in the following points.

[0181] When the thickness of the interlayer insulating film 38 is aslarge as 3 μm, for example, which is well comparable with the typicalthickness of a liquid crystal layer (a cell thickness) of 4.5 μm, lightleakage tends to occur around the contact holes 26 a and 26 b due todisturbances in the orientation of the liquid crystal molecules. If thecontact holes 26 a and 26 b are formed in the aperture portions of thetransmission type liquid crystal display device, the contrast ratio islowered due to the light leakage. In contrast, the active matrixsubstrate of this example is free from this trouble because the storagecapacitor electrode 25 a blocks the light from around the contact holes26 b and the metal electrode 23 b blocks the light from around thecontact holes 26 a. The aperture ratio can be further increased byforming the storage capacitor counter electrodes 27 so that they do notextend from the storage capacitance electrode 25 a. Though theC_(s)-Common type was used in this example, the C_(s)-on-Gate type canalso be used.

[0182] Thus, in Examples 1 to 10 above, each pixel electrode overlapsthe corresponding lines to improve the aperture ratio of the liquidcrystal display, to minimize disturbances in the orientation of theliquid crystal molecules, and to simplify the fabrication process. Also,the influence of the capacitances between the pixel electrode and thelines appearing on the display, such as crosstalk, is minimized toachieve a good display. In addition to these features, a wide viewingangle can be obtained.

[0183] The wide viewing angle can be obtained due to the followingreasons: (1) The orientation of the liquid crystal molecules is notdisturbed since the surfaces of the pixel electrodes are flat; (2) Nodisclination line is generated due to the electric field generated atthe lines; (3) oblique light from the backlight can be effectively usedby having the interlayer insulating film 38 as thick as severalmicrometers while the distance between adjacent aperture portions is inthe range of several microns to ten and several microns; and (4) Thecontrast is large (1:300 or more for a 10.4-inch SVGA). As a result, theretardation value, i.e., the refractive index anisotropy of liquidcrystal (Δn)×cell thickness (d), can be reduced. This reduction of theretardation is obtained mainly by reducing the cell thickness accordingto the present invention. In general, as the value of Δn×d decreases,the viewing angle increases but the contrast decreases. According to thepresent invention, however, the size of the pixel electrodes is madelarge by eliminating the margins conventionally provided between thepixel electrodes and the corresponding lines. For example, for a 10.4″VGA, the aperture ratio increased by about 20 points from 65% to 86%,and the brightness also increased by more than 1.5 times. For a 12.1″XGA, similarly, the aperture ratio greatly increased from 55% to 80%.The reason is as follows. In the conventional structure, when the sourceline width is 6 μm, the gap between the source line and the pixelelectrode is 3 μm, and the attachment margin is 5 μm, for example, thedistance between adjacent aperture portion is required to be 22 μm ormore. In contrast, according to the present invention where each pixelelectrode overlaps the corresponding source Lines, the distance betweenadjacent aperture portions can be 6 μm which is the source line width.Thus, the ratio of the portion which does not constitute the apertureportion to the entire area can be greatly reduced.

[0184] Examples 3 and 4 described the transmission type liquid crystaldisplay device where one electrode of the storage capacitor (a storagecapacitor electrode) is connected to the counter electrode via thestorage capacitor common line. The same effects obtained by the abovestructure can also be obtained by using the gate line 22 of the adjacentpixel as the storage capacitor electrode. FIGS. 12 and 13 show thelatter structure. This type of liquid crystal display device is called aC_(s)-on-gate type, where each pixel electrode 21 overlaps theimmediately before or next gate line 22 to form a storage capacitorC_(s). In this case, the pixel electrode 21 preferably overlaps a largerportion of the immediately before or next gate line while it overlaps asmaller portion of the corresponding gate line.

[0185] In Examples 1 to 10, the photosensitive transparent acrylic resinwith high transparency is applied by spin coating and patterned to formthe interlayer insulating film, and the contact holes are formed throughthe interlayer insulating film. The application of the photosensitivetransparent acrylic resin can also be conducted by methods other thanthe spin coating, such as roll coating and slot coating. The effects ofthe present invention can also be obtained by these methods. Rollcoating is a method where a substrate is allowed to pass through betweena roll with an uneven surface and a belt with the surface of thesubstrate to be subjected to the coating facing the roll. The thicknessof the resultant coating is determined by the degree of the unevenness.The slot coating is a method where a substrate is allowed to pass underan ejection slot. The thickness of the resultant coating is determinedby the width of the ejection slot.

[0186] In Examples 7 and 8, among the i line (wavelength: 365 nm), the hline (wavelength: 405 nm), and the g line (wavelength: 436 nm) generallyused for the light exposure process, the i line having the shortestwavelength is used. This shortens the light irradiation time, and ishighly effective in decoloring in Example 7 and in roughening thesurface in Example 8.

[0187] Thus, according to the present invention, with the existence ofthe interlayer insulating film, each pixel electrode can be formed tooverlap the corresponding lines. This improves the aperture ratio andminimizes disturbances in the orientation of the liquid crystalmolecules. Since the interlayer insulating film is composed of anorganic thin film, the dielectric constant thereof is smaller and thethickness thereof can be easily larger, compared with an inorganic thinfilm. Thus, the capacitances between the pixel electrode and the linescan be reduced. As a result, vertical crosstalk caused by thecapacitance between the pixel electrode and the source line can bereduced, and the feedthrough of the write voltage to the pixels causedby the capacitance between the pixel electrode and the gate line, aswell as the variation in the fabrication process, can be reduced.

[0188] In the formation of the interlayer insulating film, thephotosensitive organic material such as an acrylic resin is applied tothe substrate by a coating method and patterned by light exposure anddevelopment to obtain an organic thin film with a thickness of severalmicrometers with high productivity. This makes it possible to fabricatethe transmission type liquid crystal display device with a high apertureratio without largely increasing production cost. The transmission typeliquid crystal display device with a high aperture ratio can also beobtained by forming the organic thin film by deposition, forming aphotoresist on the organic thin film, and patterning the organic thinfilm in an etching process. In the case where the resin used for theinterlayer insulating film is colored, the resin can be made transparentby optically or chemically decoloring the resin after the patterning. Asa result, a good color display can be obtained.

[0189] The connecting electrode for connecting the drain electrode ofthe TFT and the pixel electrode is formed using the transparentconductive film. This further improves the aperture ratio. Thetransparent conductive film can be formed simultaneously with the sourceline which is of a double-layer structure including the transparentconductive film. With the double-layer structure, disconnection at thesource line can be prevented.

[0190] Each contact hole is formed through the interlayer insulatingfilm above the storage capacitor common line or the gate line (i.e.,scanning line). This improves the contrast ratio because light leakagewhich may be generated due to a disturbance in the orientation of theliquid crystal can be blocked by the storage capacitor portion. In otherwords, light leakage is generated in the light-shading portions, ifgenerated, not in the aperture portions.

[0191] The metal nitride layer may be formed under each contact holeformed through the interlayer insulating film. This improves theadhesion between the interlayer insulating film and the underlying film.Thus, the resultant liquid crystal display device is stable againstfurther processing in the production process.

[0192] Each pixel electrode may overlap the corresponding source line by1 μm or more. With this overlap, the aperture ratio can be maximized.Also, the processing precision of each pixel electrode with respect tothe corresponding lines is not necessarily required to be high. This isbecause, even if the processing precision is low, light leakage can bewell blocked by the overlapping lines as long as the pixel electrodeoverlaps the lines.

[0193] By having the thickness of the interlayer insulating film be 1.5μm or more (preferably, 2.0 μm or more), the capacitance between eachpixel electrode and the corresponding source line can be sufficientlysmall. This reduces the time constant even though the pixel electrodeoverlaps the source line by 1 μm or more. As a result, the influence ofthe capacitance appearing on the display, such as crosstalk, can bereduced, and thus a good display can be provided.

[0194] The vertical crosstalk is further reduced by decreasing thecapacitance ratio represented by expression (1) above to 10% or less,since the capacitance between the pixel electrode and the source line issufficiently reduced.

[0195] The polarity of the data signal supplied from the source line maybe inverted every gate line. This further reduces the influence of thecapacitance between each pixel electrode and the corresponding sourceline appearing on the display, such as vertical crosstalk.

[0196] The effects of the present invention can also be obtained for theactive matrix substrate where the pixel electrodes are arranged in avertical stripe shape and each pixel electrode is of a rectangular shapewith the side thereof parallel to the source line being longer than theside thereof parallel to the gate line. This makes it possible to obtaina large-scale liquid crystal display device with a high aperture ratiofree from vertical crosstalk for notebook type personal computers andthe like.

[0197] Each storage capacitor is formed using an insulating film whichis extremely thinner than the interlayer insulating film. The resultantstorage capacitor can have a large capacitance while the area thereof issmall. This improves the aperture ratio. Since the storage capacitorelectrodes are formed simultaneously with the source lines (i.e., signallines), an increase in the number of process steps can be avoided.

[0198] When the source lines are composed of lightshading conductivefilms, the contact hole portions can be blocked from light. Thisconceals disturbances in the orientation of the liquid crystalsoccurring at these portions, improving the display quality. This alsoimproves the aperture ratio.

[0199] In the case of using a photosensitive resin reactive toultraviolet light, if the resin has a reactive peak at the i line, thecontact holes can be formed with high precision. Also, since the peak isfarthest from the visible light, coloring can be minimized. Thisimproves the transmittance of the resultant transmission type liquidcrystal display device, and thus the amount of light from a backlightcan be reduced, saving power consumption, or the brightness can beincreased if the amount of light from the backlight is not reduced.

[0200] Since the interlayer insulating film according to the presentinvention is comparatively thick and can be made flat, conventionaltroubles caused by steps formed by the underlying lines and the like,such as disconnection on the drain side of the pixel electrode, areovercome. Disturbances in the orientation of the liquid crystal is alsoprevented. The pixel electrodes and the lines are isolated by theinterlayer insulating film formed therebetween. This greatly reduces thenumber of defective pixels due to electrical leakage between the pixelelectrodes and the lines, thereby increasing production yield andreducing production cost. Moreover, according to the present invention,the interlayer insulating film can be formed only by the resin formationstep, instead of the film formation step, the pattern formation stepwith a photoresist, the etching step, the resist removing step, and thecleaning step conventionally required. This simplifies the fabricationprocess and reduces production cost.

[0201] The entire substrate may be exposed to light to allow theremaining unnecessary photosensitive agent contained in thephotosensitive transparent acrylic resin to completely react after thelight exposure and development of the interlayer insulating film. Withthis process, an interlayer insulating film with higher transparency canbe obtained.

[0202] The surface of the substrate before the formation of theinterlayer insulating film may be irradiated with ultraviolet light.This improves the adhesion between the interlayer insulating film andthe underlying film. Thus, the resultant liquid crystal display devicecan be stable against further processing in the production process.

[0203] The surface of the interlayer insulating film may be ashed in anoxygen plasma atmosphere before the formation of the film of pixelelectrode material. This improves the adhesion of the interlayerinsulating film and the film of the pixel electrode material formedthereon. Thus, the resultant liquid crystal display device can be stableagainst further processing in the production process.

[0204] The pixel electrodes with a thickness of 50 nm or more caneffectively prevent an agent used as a removing solution from permeatingfrom gaps of the film surface into the resin and the resin fromexpanding due to the permeation of the agent.

[0205] The light irradiation time can be shortened and the decoloringefficiency is high by using the i line (wavelength: 365 nm) havinghigher energy than visible light.

[0206] As the aperture ratio of the display improves, the brightnessthereof also improves. Accordingly, the viewing angle can be widened byreducing the retardation without degrading the contrast. This makes itpossible to obtain a significantly wide viewing angle.

[0207] Various other modifications will be apparent to and can bereadily made by those skilled in the art without departing from thescope and spirit of this invention. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the description asset forth herein, but rather that the claims be broadly construed.

What is claimed is:
 1. A transmission type liquid crystal display devicecomprising: gate lines; source lines; and switching elements eacharranged near a crossing of each gate line and each source line, a gateelectrode of each switching element being connected to the gate line, asource electrode of the switching element being connected to the sourceline, and a drain electrode of the switching element being connected toa pixel electrode for applying a voltage to a liquid crystal layer,wherein an interlayer insulating film formed of an organic film withhigh transparency is provided above the switching element, the gateline, and the source line, the pixel electrode formed of a transparentconductive film is provided on the interlayer insulating film.
 2. Atransmission type liquid crystal display device according to claim 1 ,further comprising a connecting electrode for connecting the pixelelectrode and the drain electrode, wherein the interlayer insulatingfilm is provided above the switching element, the gate line, the sourceline, and the connecting electrode, the pixel electrode is formed on theinterlayer insulating film so as to overlap at least the gate line orthe source line at least partially, and the connecting electrode and thepixel electrode are connected with each other via a contact hole formedthrough the interlayer insulating film.
 3. A transmission type liquidcrystal display device according to claim 1 , wherein the interlayerinsulating film is made of a photosensitive acrylic resin.
 4. Atransmission type liquid crystal display device according to claim 1 ,wherein the interlayer insulating film is made of a resin which is madetransparent by optical or chemical decoloring treatment.
 5. Atransmission type liquid crystal display device according to claim 1 ,wherein the pixel electrode and at least one of the source line and thegate line overlap each other by 1 μm or more in a line width direction.6. A transmission type liquid crystal display device according to claim1 , wherein the thickness of the interlayer insulating film is 1.5 μm ormore.
 7. A transmission type liquid crystal display device according toclaim 2 , wherein the connecting electrode is formed of a transparentconductive film.
 8. A transmission type liquid crystal display deviceaccording to claim 2 , further comprising a storage capacitor formaintaining a voltage applied to the liquid crystal layer, wherein thecontact hole is formed above either an electrode of the storagecapacitor or the gate line.
 9. A transmission type liquid crystaldisplay device according to claim 2 , wherein a metal nitride layer isformed below the contact hole to connect the connecting electrode andthe pixel electrode.
 10. A transmission type liquid crystal displaydevice according to claim 1 , further comprising a storage capacitor forholding a voltage applied to the liquid crystal layer, wherein acapacitance ratio represented by expression (1): Capacitance ratio=C_(sd)/(C _(sd) +C _(ls) +C _(s))   (1) is 10% or less, wherein C_(sd)denotes a capacitance value between the pixel electrode and the sourceline, C_(ls) denotes a capacitance value of a liquid crystal portioncorresponding to each pixel in an intermediate display state, and C_(s)denotes a capacitance value of the storage capacitor of each pixel. 11.A transmission type liquid crystal display device according to claim 1 ,wherein the shape of the pixel electrode is rectangular with a sideparallel to the gate line being longer than a side parallel to thesource line.
 12. A transmission type liquid crystal display deviceaccording to claim 1 , further comprising a driving circuit forsupplying to the source line a data signal of which polarity is invertedfor every horizontal scanning period, and the data signal is supplied tothe pixel electrode via the switching element.
 13. A transmission typeliquid crystal display device according to claim 1 , further comprisinga storage capacitor for holding a voltage applied to the liquid crystallayer, the storage capacitor including: a storage capacitor electrode; astorage capacitor counter electrode; and an insulating filmtherebetween; wherein the storage capacitor electrode is formed in thesame layer as either the source line or the connecting electrode.
 14. Atransmission type liquid crystal display device according to claim 13 ,wherein the storage capacitor counter electrode is formed of a part ofthe gate line.
 15. A transmission type liquid crystal display deviceaccording to claim 13 , wherein the pixel electrode and the storagecapacitor electrode are connected via the contact hole formed above thestorage capacitor electrode.
 16. A transmission type liquid crystaldisplay device according to claim 13 , wherein the contact hole isformed above either the storage capacitor counter electrode or the gateline.
 17. A transmission type liquid crystal display device according toclaim 1 , wherein the interlayer insulating film is formed of aphotosensitive resin containing a photosensitive agent which has areactive peak at the i line (365 nm).
 18. A method for fabricating atransmission type liquid crystal display device, comprising the stepsof: forming a plurality of switching elements in a matrix on asubstrate; forming a gate line connected to a gate electrode of eachswitching element and a source line connected to a source electrode ofthe switching element, the gate line and the source line crossing eachother; forming a connecting electrode formed of a transparent conductivefilm connected to a source electrode of the switching element; formingan organic film with high transparency above the switching elements, thegate lines, the source lines, and the connecting lines by a coatingmethod and patterning the organic film to form an interlayer insulatingfilm and contact holes through the interlayer insulating film to reachthe connecting electrodes; and forming pixel electrodes formed oftransparent conductive films on the interlayer insulating film andinside the contact holes so that each pixel electrode overlaps at leasteither the gate line or the source line at least partially.
 19. A methodaccording to claim 18 , wherein the patterning of the organic film isconducted by either one of the following steps: exposing the organicfilm to light and developing the exposed organic film, or etching theorganic film by using a photoresist on the organic film as an etchingmask.
 20. A method according to claim 19 , wherein the patterning of theorganic film includes the steps of: forming a photoresist layercontaining silicon on the organic film; patterning the photoresistlayer; and etching the organic film by using the patterned photoresistlayer as an etching mask.
 21. A method according to claim 19 , whereinthe patterning of the organic film includes the steps of: forming aphotoresist layer on the organic film; coating a silane coupling agenton the photoresist layer and oxidizing the coupling agent; patterningthe photoresist layer; and etching the organic film by using thepatterned photoresist layer covered with the oxidized coupling agent asan etching mask.
 22. A method according to claim 20 , wherein theetching step is a step of dry etching using an etching gas containing atleast one of CF₄, CF₃H and SF₆.
 23. A method according to claim 18 ,wherein the organic film is formed by using a photosensitive transparentacrylic resin which dissolves in a developing solution when exposed tolight, and the interlayer insulating film and the contact holes areformed by exposing the photosensitive transparent acrylic resin to lightand developing the photosensitive transparent acrylic resin.
 24. Amethod according to claim 23 , further including the step of, after thelight exposure and development of the organic film, exposing the entiresubstrate to light for reacting a photosensitive agent contained in thephotosensitive transparent acrylic resin, thereby decoloring thephotosensitive transparent acrylic resin.
 25. A method according toclaim 24 , wherein a base polymer of the photosensitive transparentacrylic resin includes a copolymer having methacrylic acid and glycidylmethacrylate and the photosensitive transparent acrylic resin contains aquinonediazide positive-type photosensitive agent.
 26. A methodaccording to claim 23 , wherein the photosensitive transparent acrylicresin for forming the interlayer insulating film has a lighttransmittance of 90% or more for light with a wavelength in the range ofabout 400 nm to about 800 nm.
 27. A method according to claim 18 ,wherein the organic film has a thickness of about 1.5 μm or more.
 28. Amethod according to claim 18 , further including the step of, before theformation of the organic film, irradiating with ultraviolet light asurface of the substrate where the organic film is to be formed.
 29. Amethod according to claim 18 , further including the step of, before theformation of the organic film, applying a silane coupling agent on asurface of the substrate where the organic film is to be formed.
 30. Amethod according to claim 18 , wherein the material for forming theorganic film contains a silane coupling agent.
 31. A method according toclaim 30 , wherein the silane coupling agent includes at least one ofhexamethyl disilazane, dimethyl diethoxy silane, and n-buthyltrimethoxy.
 32. A method according to claim 18 , further including thestep of, before the formation of the pixel electrode, ashing the surfaceof the interlayer insulating film by an oxygen plasma.
 33. A methodaccording to claim 32 , wherein the ashing step is conducted after theformation of the contact holes.
 34. A method according to claim 32 ,wherein the interlayer insulating film includes a thermally curablematerial and the interlayer insulating film is cured before the ashingstep.
 35. A method according to claim 32 , wherein the thickness of theashed portion of the interlayer insulating film is in the range of about100 to 500 nm.
 36. A method according to claim 18 , wherein thethickness of the pixel electrode is about 50 nm or more.
 37. A methodaccording to claim 25 , wherein the interlayer insulating film is formedby developing the photosensitive transparent acrylic resin withtetramethyl ammonium hydroxyoxide developing solution with aconcentration of about 0.1 mol % to about 1.0 mol %.
 38. A methodaccording to claim 23 , further including the step of, after theformation of the contact holes through the interlayer insulating film,decoloring the interlayer insulating film by irradiating the interlayerinsulating film with ultraviolet light.
 39. A method according to claim23 , further including the step of, before the formation of the organicfilm, forming a silicon nitride film on a surface of the substrate wherethe organic film is to be formed.